Pseudouridine, the 5-ribosyl isomer of uridine, is the most common post-transcriptional modification known in RNA molecules. The ribosome of the model eubacterum Escherichia coli has eleven pseudouridines; 10 in the 23S RNA and 1 in the 16S RNA. These pseudouridines are formed by 7 site-specific pseudouridine synthases with no overlapping specificity. The effect of deleting any one synthase gene is loss of the pseudouridine(s) that it forms. Thus far, no pseudouridine specific growth defect has been detected. We plan to make a strain carrying 4 synthase gene deletions and lacking 6 pseudouridines to investigate the structural and/or functional differences of these pseudouridine deficient ribosomes from normal ribosomes. These differences may provide insight into the function of pseudouridine in the ribosome. In addition, we plan to map the positions of pseudouridien in the ribosome of deinococcus radiodurans because the cyrstal structure of its 50S ribosomal subunit is available and we can model the positions of pseudouridines in 3D space for possible insights into function based on structure. In ribosomes, pseudouridines tend to cluster around the peptidyl transferase center which may implicate a structural and/or functional role in translation - which is crucial to the well-being of all organisms. If pseudouridines do participate in translation, then we may have a new antibiotic target because the mechanism of ribosomal pseudouridine formation in humans differs from that of bacteria.